The present invention relates to methods of inhibiting growth and reproduction of microorganisms in rapidly biodegradable hydrocarbonaceous products, containing minor amounts of aqueous liquids. The present invention also relates to rapidly biodegradable hydrocarbonaceous products containing an effective amount of a petroleum-derived hydrocarbonaceous product such that the rapidly biodegradable hydrocarbonaceous product resists visible growth of microorganisms.
Certain microbiological problems may arise with respect to the storage and transportation of hydrocarbonaceous products. Hydrocarbons can act as a nutrient for microorganisms; therefore, hydrocarbonaceous products (i.e., fuels such as jet fuel, diesel fuel, naphtha; lubes, and solvents) can be attacked by microorganisms. Microorganisms can slowly grow at the boundary layers of the hydrocarbonaceous product and air, and can grow more rapidly if the hydrocarbonaceous product is also exposed to a layer of water.
Hydrocarbonaceous products are frequently exposed to a layer of water when stored in large storage vessels, such as storage tanks, fuel tanks of aircraft and holds of tankers. In these large storage vessels, water invariably forms due to condensation or it is initially present in the stored hydrocarbonaceous product and slowly separates therefrom. This water gradually forms a layer in the bottom of the storage vessels. The water layer forms an interface with the hydrocarbonaceous product, and becomes a breeding ground for a wide variety of microorganisms. These microorganisms utilize the hydrocarbonaceous product as a nutrient and can multiply.
Eventually the microorganisms can consume a large portion of the hydrocarbonaceous product. The extent to which the microorganisms consume the product is known as the extent of biodegradation, or the biodegradability of the product.
The microorganisms or microbes will grow mostly in the water phase, but when the hydrocarbonaceous product is disturbed during pumping or mixing, the microbes can be dispersed into the hydrocarbonaceous product and cause contamination. When present in the hydrocarbonaceous product, microbial growth can present a problem for several reasons. For example, hydrocarbonaceous products may become contaminated with microbes during storage or shipment and as a result of the microbes, become hazy or cloudy. The growing microorganisms may form sludge in the contaminated hydrocarbonaceous product. When contaminated hydrocarbonaceous products are used in an engine or equipment, the microbes and/or the sludge may decrease the efficiency of the engine or equipment or prevent it from functioning altogether, for example, by plugging filters. In addition, growth of microorganisms, in particular anaerobic sulfate reducing bacteria, in hydrocarbonaceous products during storage or transport may create corrosive sulfur-containing acids and damage the vessels in which the products are contained. This corrosion damage may lead to the need for eventual replacement of these large, expensive vessels.
Further, transport of hydrocarbonaceous products and/or a water layer contaminated with microbes creates a dispersal mechanism for human pathogens, waterborne diseases of plants and animals, and foreign organisms into the environment. For example, infectious bacteria such as cholera have been found in ballast water from marine tankers (xe2x80x9cGlobal Spread of Microorganisms By Ships,xe2x80x9d Brief Communications Nov. 2, 2000 issue of Nature). These infectious organisms can create both a human health problem, and a health problem to native species in the receiving country. Water can also be the vehicle for the introduction of foreign higher life forms into the receiving countries"" environment. By this route, Zebra clams are believed to have been introduced into the San Francisco Bay region.
There is a need for hydrocarbonaceous products comprising rapidly biodegradable hydrocarbonaceous products that are capable of resisting visible growth of microorganisms and methods of inhibiting the growth and reproduction of microorganisms in rapidly biodegradable hydrocarbonaceous products, containing minor amounts of aqueous liquids.
The invention relates to hydrocarbonaceous products comprising rapidly biodegradable hydrocarbonaceous products that are capable of resisting visible growth of microorganisms. One aspect of the present invention is a hydrocarbonaceous product comprising: a) a rapidly biodegradable hydrocarbonaceous product; and b) an effective amount of a petroleum-derived hydrocarbonaceous product such that the resulting hydrocarbonaceous product resists visible growth of microorganisms for at least 10 days under ambient conditions when exposed to a certified inoculant. The rapidly biodegradable hydrocarbon product may include, for example, a Fischer-Tropsch derived liquid product or a low aromatics diesel fuel. When the rapidly biodegradable product is a Fischer-Tropsch derived liquid product, the Fischer-Tropsch product preferably may be one that has a branching index of less than five.
An additional aspect of the present invention is a method of inhibiting growth and reproduction of microorganisms in rapidly biodegradable hydrocarbonaceous products, containing minor amounts of aqueous liquids. The method comprises:
a) providing a rapidly biodegradable hydrocarbonaceous product;
b) adding an effective amount of a petroleum-derived hydrocarbonaceous product to resist visible growth of microorganisms for at least 10 days under ambient conditions when exposed to a certified inoculant; and
c) mixing the petroleum-derived hydrocarbonaceous product into the rapidly biodegradable hydrocarbonaceous product.
The method may also comprise the step of processing the mixture with hydrogen (i.e., hydrotreating, hydrocracking, and hydroisomerization) to remove sulfur and other impurities that originate from the conventional fuel component after the period in which growth is expected.
Definitions
Unless otherwise stated, the following terms used in the specification and claims have the meanings given below:
xe2x80x9cBiocidesxe2x80x9d mean chemical compounds that kill or inhibit the growth of microorganisms, such as for example, bacteria, molds, slimes, fungi, and the like.
xe2x80x9cBranching indexxe2x80x9d means a numerical index for measuring the average number of side chains attached to a main chain of a compound. For example, a compound that has a branching index of two means a compound having a straight chain main chain with an average of approximately two side chains attached thereto. The branching index of a product of the present invention may be determined as follows. The total number of carbon atoms per molecule is determined. A preferred method for making this determination is to estimate the total number of carbon atoms from the molecular weight. A preferred method for determining the molecular weight is Vapor Pressure Osmometry following ASTM D-2503, provided that the vapor pressure of the sample inside the Osmometer at 45xc2x0 C. is less than the vapor pressure of toluene. For samples with vapor pressures greater than toluene, the molecular weight is preferably measured by benzene freezing point depression. Commercial instruments to measure molecular weight by freezing point depression are manufactured by Knauer. ASTM D-2889 may be used to determine vapor pressure. Alternatively, molecular weight may be determined from an ASTM D-2887 or ASTM D-86 distillation by correlations which compare the boiling points of known n-paraffin standards.
xe2x80x9cFischer-Tropsch derived liquid products mean hydrocarbonaceous, liquid products derived from a Fischer-Tropsch process. Fischer-Tropsch derived liquid products include, for example, Fischer-Tropsch naphtha, Fischer-Tropsch jet fuel, Fischer-Tropsch diesel fuel, Fischer-Tropsch solvent, Fischer-Tropsch lube base stock, Fischer-Tropsch lube base oil, Fischer-Tropsch lube base oil feedstock and mixtures thereof.
xe2x80x9cHydrocarbonaceousxe2x80x9d means containing hydrogen and carbon atoms and potentially also containing heteroatoms, such as oxygen, sulfur, nitrogen, and the like.
xe2x80x9cHydrocarbonaceous Productxe2x80x9d means any hydrocarbonaceous product, including both conventional or petroleum-derived hydrocarbonacous products and those identified as rapidly biodegradable hydrocarbonaceous products. Hydrocarbonaceous products contain hydrogen and carbon atoms and may also contain heteroatoms, such as oxygen, sulfur, nitrogen, and the like.
xe2x80x9cParaffinxe2x80x9d means any saturated hydrocarbon compound, i.e., an alkane with a chemical formula of CnH2n+2.
xe2x80x9cPetroleum-Derived Hydrocarbonaceous Productxe2x80x9d means any hydrocarbonaceous product that is derived from conventional petroleum products and that exhibits virtually no visual growth of microorganisms in approximately ten days or less. Petroleum-derived hydrocarbonaceous products may be derived from, for example, conventional petroleum, conventional diesel fuel, conventional solvent, conventional jet fuel, conventional naphtha, conventional lube base stock, conventional lube base oil, lube base oil feedstock and mixtures thereof.
xe2x80x9cRapidly Biodegradable Hydrocarbonaceous Productxe2x80x9d means a hydrocarbonaceous product in which visual growth of microorganisms occurs in approximately ten days or less. Rapidly biodegradable hydrocarbonaceous products may include, for example, Fischer-Tropsch derived liquid products and low aromatics diesel fuel. Rapidly biodegradable hydrocarbonaceous products of the present invention preferably are Fischer-Tropsch derived liquid products.
Hydrocarbonaceous products are typically stored or transported for a period of time before use, generally at least ten days. During storage and/or transport, minor amounts of aqueous liquids invariably form due to condensation or are initially present in the stored hydrocarbonaceous product and slowly separate therefrom. Minor amounts of aqueous liquids typically include between 0.01% and 25% aqueous liquid.
While high levels of biodegradability are ultimately desirable for hydrocarbonaceous products, rapid biodegradation during storage and transport is not desirable. Biodegradation during transport and storage and prior to use may cause many problems, as described previously.
Certain hydrocarbonaceous products now have been identified that not only are subject to biodegradation, but are also subject to rapid biodegradation. These xe2x80x9crapidly biodegradable hydrocarbonaceous productsxe2x80x9d may show visual growth of microorganisms in approximately ten days or less. The unusual speed of biodegradation of these certain hydrocarbonaceous products has not previously been recognized.
Products identified as rapidly biodegradable hydrocarbonaceous products in the present invention may include, for example, Fischer-Tropsch derived liquid products and Low Aromatics Diesel Fuel. Preferably, the rapidly biodegradable hydrocarbonaceous products of the present invention are Fischer-Tropsch derived liquid products, and more preferably, are Fischer-Tropsch derived liquid products having a branching index less than five.
It has now been determined that commercial use of Fischer-Tropsch hydrocarbonaceous products and other rapidly biodegradable hydrocarbonaceous products creates an increased need for control of biological degradation. In conventional hydrocarbonaceous products, various compounds, such as aromatics, and heteroatoms, such as sulfur, nitrogen, and the like, are present. These compounds and heteroatoms tend to be natural biocides or microbial inhibitors, and thus may naturally inhibit the growth of the microbes in conventional hydrocarbonaceous products. Therefore, when using conventional hydrocarbonaceous products, the products can be shipped and stored for a period of time. However, when using hydrocarbonaceous products identified as rapidly biodegradable, it has now been determined that special measures must be taken to avoid problems resulting from rapid biodegradation during shipment and storage of these products to prevent biological degradation and microbial growth.
A product may be identified as rapidly biodegradable if visual growth of microorganisms occurs in the product in approximately ten days or less. Visual growth or formation of microorganisms may be measured quantitatively by measuring turbidity of the product in question. Turbidity is generally measured by using a turbidity meter, for example, a Hach Co. Model 2100 P Turbidimeter. A turbidity meter is a nephelometer that consists of a light source that illuminates a water/oil sample and a photoelectric cell that measures the intensity of light scattered at a 90xc2x0 angle by the particles in the sample. A transmitted light detector also receives light that passes through the sample. The signal output (units in nephelometric turbidity units or NTUs) of the turbidimeter is a ratio of the two detectors. Meters can measure turbidity over a wide range from 0 to 1000 NTUs. The instrument must meet US-EPA design criteria as specified in US-EPA method 180.1.
By way of example, typical lube base oils measured at 75xc2x0 F. have ranges of from 0 to 20 NTUs. Commercial Poly Alpha Olefins (PAOs) tend to have NTUs between 0 and 1. The visual formation of microorganisms is said to occur when the NTU value increases by two units from measurements made before and after microorganisms or inoculant are introduced into the sample. Measurements are made on the aqueous phase in contact with the hydrocarbon. Therefore, the NTU value of the rapidly biodegradable hydrocarbonaceous products of the present invention may show an increase of two or more units in approximately ten days or less after introduction of an inoculant.
Fischer-Tropsch Process
The majority of combustible fuel used in the world today is derived from crude oil. There are several limitations to using crude oil as a fuel source. Crude oil is in limited supply; it includes aromatic compounds that may be harmful, and contains sulfur and nitrogen-containing compounds that can adversely affect the environment, for example, by producing acid rain.
Combustible liquid fuels can also be prepared from natural gas. This preparation involves converting the natural gas, which is mostly methane, to synthesis gas, or syngas, which is a mixture of carbon monoxide and hydrogen. An advantage of using fuels prepared from syngas is that they do not contain nitrogen and sulfur and generally do not contain aromatic compounds. Accordingly, they have minimal health and environmental impact. These Fischer-Tropsch derived fuels are considered xe2x80x9cgreen fuelsxe2x80x9d and are desirable as environmentally friendly.
Fischer-Tropsch chemistry is typically used to convert the syngas to a product stream that includes combustible fuel, among other products. A preferred rapidly biodegradable hydrocarbonaceous product is one derived from the Fisher-Tropsch process. A preferred Fischer-Tropsch product of the present invention has a branching index of less than five.
Fischer-Tropsch (FT) derived products include, for example, Fischer-Tropsch naphtha, Fischer-Tropsch jet fuel, Fischer-Tropsch diesel fuel, Fischer-Tropsch solvent, Fischer-Tropsch lube base stock, Fischer-Tropsch lube base oil, Fischer-Tropsch lube base oil feedstock and mixtures thereof. Distillate fuels, derived from the Fischer-Tropsch process, have excellent burning properties. Fischer-Tropsch products contain essentially no aromatics or heteroatoms, such as sulfur and nitrogen. In addition, Fischer-Tropsch distillate fuels are highly paraffinic; paraffins are the majority components ( greater than 50%) and can exceed 70% and even 95%. As a class, paraffins are the most biodegradable compounds found in petroleum and are preferentially metabolized by microbes. Alkane oxygenases are the enzymes that initiate paraffin (i.e. alkane) degradation.
In contrast to Fischer-Tropsch products, petroleum-derived or conventional hydrocarbonaceous products contain many components, and paraffins are only a minority component.
Since Fischer-Tropsch products contain essentially no natural biocides (i.e., aromatics, nitrogen, sulfur) and contain paraffins as a majority component, Fischer-Tropsch products are biodegradable. It has now been determined that Fischer-Tropsch products are also rapidly biodegradable, and therefore, are more susceptible to biodegradation during normal transport and storage than comparable petroleum fractions. The greater susceptibility for biodegradation of Fischer-Tropsch products increases the need for effective biocides during shipment and storage of these products.
Fischer-Tropsch products also tend to oxidize relatively rapidly when exposed to air. The rapid oxidation may be due to a lack of natural anti-oxidants, such as sulfur compounds.
Catalysts and conditions for performing Fischer-Tropsch synthesis are well known to those of skill in the art, and are described, for example, in EP 0 921 184 A1, the contents of which are hereby incorporated by reference in their entirety. In the Fischer-Tropsch synthesis process, liquid and gaseous hydrocarbons are formed by contacting a synthesis gas (syngas) comprising a mixture of H2 and CO with a Fischer-Tropsch catalyst under suitable temperature and pressure reactive conditions. The Fischer-Tropsch reaction is typically conducted at temperatures of from about 300xc2x0 to 700xc2x0 F. (149xc2x0 to 371xc2x0 C.) preferably from about 400xc2x0 to 550xc2x0 F. (204xc2x0 to 228xc2x0 C.); pressures of from about 10 to 600 psia, (0.7 to 41 bars) preferably 30 to 300 psia, (2 to 21 bars) and catalyst space velocities of from about 100 to 10,000 cc/g/hr., preferably 300 to 3,000 cc/g/hr.
The products may range from C1 to C200+ with a majority in the C5 to C100+ range. The reaction can be conducted in a variety of reactor types, for example, fixed bed reactors containing one or more catalyst beds; slurry reactors; fluidized bed reactors; and a combination of different type reactors. Such reaction processes and reactors are well known and documented in the literature. Slurry Fischer-Tropsch processes, which are a preferred process in the practice of the invention, utilize superior heat (and mass) transfer characteristics for the strongly exothermic synthesis reaction and are able to produce relatively high molecular weight, paraffinic hydrocarbons when using a cobalt catalyst.
In a slurry process, a syngas comprising a mixture of H2 and CO is bubbled up as a third phase through a slurry in a reactor which comprises a particulate Fischer-Tropsch type hydrocarbon synthesis catalyst dispersed and suspended in a slurry liquid comprising hydrocarbon products of the synthesis reaction which are liquid at the reaction conditions. The mole ratio of the hydrogen to the carbon monoxide may broadly range from about 0.5 to 4, but is more typically within the range of from about 0.7 to 2.75 and preferably from about 0.7 to 2.5. A particularly preferred Fischer-Tropsch process is taught in EP 0609079, herein incorporated by reference in its entirety.
Suitable Fischer-Tropsch catalysts comprise one or more Group VIII catalytic metals such as Fe, Ni, Co, Ru and Re. Additionally, a suitable catalyst may contain a promoter. Thus, a preferred Fischer-Tropsch catalyst comprises effective amounts of cobalt and one or more of Re, Ru, Pt, Fe, Ni, Th, Zr, Hf, U, Mg and La on a suitable inorganic support material, preferably one which comprises one or more refractory metal oxides. In general, the amount of cobalt present in the catalyst is between about 1 and about 50 weight percent of the total catalyst composition. The catalysts can also contain basic oxide promoters such as ThO2, La2O3, MgO, and TiO2, promoters such as ZrO2, noble metals (Pt, Pd, Ru, Rh, Os, Ir), coinage metals (Cu, Ag, Au), and other transition metals such as Fe, Mn, Ni, and Re. Support materials including alumina, silica, magnesia and titania or mixtures thereof may be used. Preferred supports for cobalt containing catalysts comprise titania. Useful catalysts and their preparation are known and illustrative, but non-limiting examples may be found, for example, in U.S. Pat. No. 4,568,663.
Resistance to Microbial Growth
In order to combat microbial growth and degradation of hydrocarbonaceous products, the products and/or the water layer in contact with the products may be treated with a biocide. See for example, U.S. Pat. Nos. 3,393,058 and 4,086,066. Biocides are chemical compounds that kill or inhibit the growth of microorganisms, such as for example, bacteria, molds, slimes, fungi, and the like. Biocides typically inhibit growth in hydrocarbonaceous products while being contained in the water layer. See for example U.S. Pat. No. 4,086,066.
However, the use of biocides in hydrocarbonaceous products may cause disposal and wastewater problems. Due to a biocide""s potential continuing antimicrobial effects, water that contacts or contains biocides should not be discharged directly into the environment. Upon direct release into the environment, the biocide may kill or inhibit the growth of indigenous, and potentially desirable, bacterial, molds, fungi, and higher life forms. Therefore, the biocides may contaminate or pollute water supplies or require costly water treatment measures before disposal.
Further, the biocide may complicate necessary treatment of bilge water to remove residual hydrocarbons. For example, upon unloading of the hydrocarbonaceous products, the water that contacted the product may be contaminated with residual hydrocarbons. Therefore, this bilge water must be treated in on-shore facilities to remove hydrocarbons. For example, the water may be treated in a biological oxidation facility to remove residual hydrocarbons. Biocides present in the bilge water may make this treatment even more difficult and expensive. In addition, when the hydrocarbonaceous product is used for its intended purpose, residual biocide in the product may be introduced into the environment.
Therefore, there is a need for agents that are capable of inhibiting visible growth of microorganisms in rapidly biodegradable hydrocarbonaceous products that do not have the disadvantages of conventional biocides. It also important that these agents be compatible with the rapidly biodegradable hydrocarbonaceous products of the present invention.
It has now been determined that growth of microorganisms in rapidly biodegradable hydrocarbonaceous products may be inhibited by mixing the rapidly biodegradable products with an effective amount of a petroleum-derived hydrocarbonaceous product. Petroleum-derived hydrocarbonaceous products may act as an agent capable of inhibiting visible growth of microorganisms in rapidly biodegradable hydrocarbonaceous products. Therefore, to inhibit visible growth of microorganisms in rapidly biodegradable hydrocarbonaceous products, the rapidly biodegradable hydrocarbonaceous product may be mixed with an effective amount of a petroleum-derived hydrocarbonaceous product to provide a blended product.
The resulting blended product may resist visible growth of microorganisms for at least 10 days under ambient conditions when exposed to a certified inoculant. Therefore, the resulting blended product may be safely stored or transported without the use of additional conventional biocides or with the use of much lower levels of additional conventional biocides.
An effective amount of petroleum-derived hydrocarbonaceous product is the amount that inhibits microbial growth in a rapidly biodegradable hydrocarbonaceous product for approximately 10 days. The effective amount of petroleum derived hydrocarbonaceous product may vary, and thus the exact concentration of petroleum-derived hydrocarbonaceous product in the resulting blended product will also vary. Generally, the petroleum-derived hydrocarbonaceous product may be added in a concentration of approximately 10 to 90 wt %, more preferably 25 to 75 wt %. Most preferably the petroleum-derived hydrocarbonaceous product may be added in a concentration of approximately 30 to 50 wt %. It is preferable to add the petroleum-derived hydrocarbonaceous product in as low of a concentration as possible and still effectively inhibit microbial growth.
Petroleum-derived hydrocarbonaceous products are desirable agents for inhibiting growth of microorganisms in the present invention due to their high compatibility with the rapidly biodegradable hydrocarbonaceous products, including Fischer-Tropsch derived products. Petroleum-derived hydrocarbonaceous products may be highly compatible and particularly effective in inhibiting growth in the rapidly biodegradable hydrocarbonaceous products of the present invention because they reside blended in with the rapidly biodegradable hydrocarbonaceous product not as conventional biocides in the water layer.
Further, to avoid these environmental and treatment concerns, petroleum-derived hydrocarbonaceous products are preferred for use in the present invention to inhibit growth of microorganisms. When using petroleum-derived hydrocarbonaceous products to inhibit growth, the water layer may be removed and directly released or recycled without danger of environmental problems, or the water may be treated in an on-shore facility, for example a biological oxidation facility, to remove residual hydrocarbons without added expense or complications due to the biocide.
Therefore, the rapidly biodegradable hydrocarbonaceous products of the present invention may be blended with a petroleum-derived hydrocarbonaceous product during storage and/or transportation to inhibit growth of microorganisms.
Methods of Inhibiting the Growth and Reproduction of Microorganisms in Hydrocarbonaceous Products
The present invention also relates to methods of inhibiting the growth and reproduction of microorganisms in rapidly biodegradable hydrocarbonaceous products containing minor amounts of aqueous liquids. In the method of the present invention, a rapidly biodegradable hydrocarbonaceous product is provided. An effective amount of petroleum-derived hydrocarbon product is added. The petroleum-derived hydrocarbon product is mixed into the rapidly biodegradable hydrocarbon product. An effective amount of petroleum-derived hydrocarbon product means that the resulting blended product is capable of resisting visible growth of microorganisms for at least 10 days under ambient conditions when exposed to a certified inoculant.
Resisting visible growth for at least 10 days means that the visual formation of microorganisms does not occur for at least 10 days. As explained previously, visual growth of microorganisms is said to occur when the NTU value increases by two units from measurements made before and after the inoculant is introduced into the sample. Therefore, resisting visual growth for at least 10 days means that the NTU value does not increase by two units. A certified inoculant consists of a source of bacteria initially isolated at ambient conditions using a rapidly biodegradable hydrocarbanaceous product standard, such as nC16, as the sole source of carbon and energy, and that has been shown to grow on the hydrocarbanaceous product through two or more successive inoculations. Ambient conditions mean a temperature between 10 and 40xc2x0 C. and a pH between 6 and 8.5.
The method may also comprise the step of processing the blended mixture to remove or at least reduce any impurities, aromatics and heteroatom (such as sulfur, nitrogen, metals) content after the period in which growth is expected.
The present invention preferably relates to a method of inhibiting the growth and reproduction of microorganisms in Fischer-Tropsch derived liquid products, preferably Fischer-Tropsch derived liquid products having a branching index of less than five. In this method of the present invention, a Fischer-Tropsch derived liquid product is synthesized in a Fischer-Tropsch synthesis process from a suitable synthesis gas. The product recovered from a Fischer-Tropsch process may range from C5 to C20+, distributed in one or more product fractions.
The products from Fischer-Tropsch reactions performed in slurry bed reactors generally include a light reaction product and a waxy reaction product. The light reaction product (i.e. the condensate fraction) includes hydrocarbons boiling below about 700xc2x0 F. (e.g., tail gases through middle distillates), largely in the C5-C20 range, with decreasing amounts up to about C30. The waxy reaction product (i.e. the wax fraction) includes hydrocarbons boiling about 600xc2x0 F. (e.g., vacuum gas oil through heavy paraffins), largely in the C20+ range, with decreasing amounts down to C10. Both the light reaction product and the waxy product are substantially paraffinic. The waxy product generally comprises greater than 70% normal paraffins, and often greater than 80% normal paraffins. The light reaction product comprises paraffinic products with a significant proportion of alcohols and olefins. In some cases, the light reaction product may comprise as much as 50%, and even higher, alcohols and olefins.
The product from the Fischer-Tropsch process may be further processed using, for example, hydrocracking, hydroisomerization, hydrotreating. Such processes crack the larger synthesized molecules into fuel range and lube range molecules with more desirable boiling points, pour points, and viscosity index properties. Such processes may also saturate oxygenates and olefins to meet the particular needs of a refiner. These processes are well known in the art and do not require further description here.
To the Fischer-Tropsch derived liquid product is added an effective amount of petroleum-derived hydrocarbon product. An effective amount of petroleum-derived hydrocarbon product means that the resulting blended product is capable of resisting visible growth of microorganisms for at least 10 days under ambient conditions when exposed to a certified inoculant. The petroleum-derived hydrocarbon product is mixed into the Fischer-Tropsch derived liquid product.
A desirable property of Fischer-Tropsch products is that they contain essentially no aromatics or heteroatoms, such as sulfur and nitrogen. Therefore, Fischer-Tropsch liquid products may be used as environmentally friendly green fuels. However, the petroleum derived hydrocarbonaceous products, added to the Fischer-Tropsch products to inhibit growth of microorganisms, may add impurities, aromatics, and unwanted heteroatoms (such as sulfur and nitrogen). Therefore, the resulting blended product may contain impurities, aromatics, and unwanted heteroatoms that the original Fischer-Tropsch product did not contain.
Accordingly, after the period in which biological growth is expected and before the Fischer-Tropsch liquid products are used, it may be desirable to remove or at least reduce the impurities, aromatics, and unwanted heteroatoms (such as sulfur, nitrogen, metals). The impurities, aromatics, and heteroatom content may be reduced by a number of processes. These processes may include hydrotreating, hydrocracking, hydroisomerization, extraction, adsorption, and the like. The preferred methods are those involving processing with hydrogen (i.e., hydrotreating, hydrocracking, and hydroisomerization), with hydrotreating being the most preferred.
Hydrotreating is a process for removing impurities, such as heteroatoms (i.e. sulfur, nitrogen, oxygen) or compounds containing sulfur, nitrogen, or oxygen, from a hydrocarbon product mixture. Typical hydrotreating conditions vary over a wide range. In general, the overall LHSV (Liquid Hourly Space Velocity) is about 0.25 to 2.0 hrxe2x88x921, preferably about 0.5 to 1.0 hrxe2x88x921. The hydrogen partial pressure is greater than 200 psia, preferably ranging from about 500 psia to about 2500 psia. Hydrogen re-circulation rates are typically greater than 50 SCF/Bbl, and are preferably between 1000 and 5000 SCF/Bbl. Temperatures range from about 300xc2x0 F. to about 750xc2x0 F., preferably ranging from 450xc2x0 F. to 600xc2x0 F.
Accordingly, the methods of the present invention may also comprise the step of processing the blended mixture to remove or at least reduce any impurities, aromatics, and heteroatoms (such as sulfur, nitrogen, metals) originating from the petroleum derived product. The processing step may involve hydrotreating, hydrocracking, hydroisomerization, extraction, adsorption, and the like, preferably hydrotreating.
The branching index of a product of the present invention may be determined as follows. The total number of carbon atoms per molecule is determined. A preferred method for making this determination is to estimate the total number of carbon atoms from the molecular weight. A preferred method for determining the molecular weight is Vapor Pressure Osmometry following ASTM-2503, provided that the vapor pressure of the sample inside the Osmometer at 45xc2x0 C. is less than the vapor pressure of toluene. For samples with vapor pressures greater than toluene, the molecular weight is preferably measured by benzene freezing point depression. Commercial instruments to measure molecular weight by freezing point depression are manufactured by Knauer. ASTM D2889 may be used to determine vapor pressure. Alternatively, molecular weight may be determined from a ASTM D-2887 or ASTM D-86 distillation by correlations which compare the boiling points of known n-paraffin standards.
The fraction of carbon atoms contributing to each branching type is based on the methyl resonances in the carbon NMR spectrum and uses a determination or estimation of the number of carbons per molecule. The area counts per carbon is determined by dividing the total carbon area by the number of carbons per molecule. Defining the area counts per carbon as xe2x80x9cAxe2x80x9d, the contribution for the individual branching types is as follows, where each of the areas is divided by area A:
2-branches=half the area of methyls at 22.5 ppm/A
3-branches=either the area of 19.1 ppm or the area at 11.4 ppm (but not both)/A
4-branches=area of double peaks near 14.0 ppm/A
4+ branches=area of 19.6 ppm/A minus the 4-branches internal ethyl branches=area of 10.8 ppm/A
The total branches per molecule (i.e. the branching index) is the sum of areas above.
For this determination, the NMR spectrum is acquired under the following quantitative conditions: 45 degree pulse every 10.8 seconds, decoupler gated on during 0.8 sec acquisition. A decoupler duty cycle of 7.4% has been found to be low enough to keep unequal Overhauser effects from making a difference in resonance intensity.
In a specific example, the molecular weight of a Fischer-Tropsch Diesel Fuel sample, based on the 50% point of 478xc2x0 F. and the API gravity of 52.3, was calculated to be 240. For a paraffin with a chemical formula CnH2n+2, this molecular weight corresponds to an average number n of 17.
The NMR spectrum acquired as described above had the following characteristic areas:
2-branches=half the area of methyl at 22.5 ppm/A=0.30
3-branches=area of 19.1 ppm or 11.4 ppm not both/A=0.28
4-branches=area of double peaks near 14.0 ppm/A=0.32
4+ branches=area of 19.6 ppm/A minus the 4-branches=0.14 internal ethyl branches=area of 10.8 ppm/A=0.21
The branching index of this sample was found to be 1.25.